Nonlinear heart rate variability in CABG patients and the preconditioning effect

Abstract

Heart rate variability (HRV) is the most frequently used noninvasive diagnostic method in the assessment of cardiac autonomic control. The clinical relevance of HRV, especially nonlinear HRV in CPB patients has not been well studied. Short brief myocardial ischemia has been reported to influence HRV. We therefore hypothesis that the protective mechanism of ischemic preconditioning (IP) may involve in cardiac autonomic regulation. Eighty-six CABG patients were randomized into a control and an IP group. The IP patients received two periods of 2-min ischemia followed by 3-min reperfusion by aortic cross-clamped. Holter data were collected in 86 CABG patients before and after surgery. Arrhythmias, linear and nonlinear HRV measures were analyzed. All time and frequency domain HRV variables as well as nonlinear indexes of HRV, the short-term (4-11 beats) scaling exponent alpha1, were suppressed significantly after surgery in both study groups. The lower pre- and postoperative exponent alpha1 predict the higher incidence of postoperative AF and worse postoperative outcome. The suppressed exponent alpha1 was attenuated in the IP group as compared to controls (P = 0.008). No other differences were observed in the changes in linear HRV measures between the groups. IP significantly reduced the incidence of postoperative arrhythmias and improved postoperative outcome. The present findings show that cardiac autonomic regulation is impaired after CABG. Nonlinear HRV exponent alpha1 is a more sensitive measure to predict the postoperative outcome in CABG patients. IP alleviates the extreme autonomic reactions after surgery, suggesting that cardiac autonomic regulation is involved in the IP protective mechanism.